html {
  margin: 0;
}

span {
  display: block;
}
.canvas {
  margin: 100px auto 100px;
  width: 80%;
  text-align: center;
}

.button {
  width: 100px;
  height: 100px;
  border: solid #000 2px;
  display: inline-block;
}

#grey {
  background: grey;
}

#green {
  background: green;
}
#blue {
  background: blue;
}
#yellow {
  background: yellow;
}
.randombtn {
  padding: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
}
.randombtn button {
  border-radius: 30px;
  padding: 20px;
  background-color: transparent;
}